I have just recently purchased a crown XLS1500 amplifier to be used with my Onkyo 875 receiver to power my front M80s. I didn't realize that the amp could only work with a 120 volt power supply. I only have 240 volt where I live. I then decided to try a cheap step down transformer to step 240v down to 120v. Suprising that this crown XLS1500 amp only draws max 250 watts yet claims to put out over 500 watts/channel into 4 ohms. Anyway that is a separate story.With everything connected up I am getting a low frequency hum from the fronts. When I disconnect the rca input to the crown the hum disappears. It is only present when the onkyo receiver is on and the pre-amp out is connected to the crown amp.Is there any way I can eliminate this hum or reduce it.Should I use the XLR inputs on the Crown. To do this I would need to get an RCA to XLR adaptor. Is it possible this hum is caused by the step down transformer? I doubt it since the hum is not always present. Any ideas?

Should I use the XLR inputs on the Crown. To do this I would need to get an RCA to XLR adaptor. Is it possible this hum is caused by the step down transformer? I doubt it since the hum is not always present. Any ideas?

To get the true benefit of XLR connectors you're receiver/processor would have to have XLR outs... XLR's are a 3 wire system, RCA is a 2 wire system... To get rid of the hum, you need a true 3 wire system.

I had the same problem, i think it's the wiring in my house.. I am using all XLR connectors. However, my processor has XLR outputs....

By using a step down transformer, are isolating that outlet. My money is on a ground loop problem. My house also have a ground loop... So, i have to deal with multiple electrical issues.....

I disconnected all inputs to the receiver but no difference however I just disconnected the hdmi out from the receiver and the hum is significantly reduced. Still annoying but much better. But I need to use this HDMI output.